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La pedrera Reservoir


La Pedrera Reservoir has the function of regulating part of the flows transported by the Left Bank Distribution Canal to meet the irrigation demands of Campo de Cartagena and to supply a series of towns and villages in its territorial environment, managed through the Mancomunidad de los Canales del Taibilla. Its reduced catchment area and its small flows would never have justified the construction of this reservoir, which is practically used as a regulating reservoir. It is a masterpiece of the distribution of the water coming from the Tagus-Segura Aqueduct through the Distribution Canals, and practically all its inflows come from the Tagus-Segura Joint Exploitation. This work started to take form during the I Economic and Social Development Plan (1964-67) –the beginning of the preliminary plan -, although it was not until the II Development Plan (1968-71) that it was finally defined technically and the works began, under the ministry of Federico Silva Muñoz.

In September 1967 La Pedrera Reservoir started to be studied in a regular way along with the Tagus-Segura Aqueduct. From the first moment this reservoir was assigned the function of being a regulating reservoir for the internal distribution of the water coming from the Tagus, for storing the volumes with which the Campo de Cartagena would be irrigated and for supplying a series of towns and villages of the Baja Vega del Segura, in the province of Alicante.

La Pedrera Reservoir Picture

The main dam of La Pedrera is a gravity one, with a straight ground plan, and of earth construction with a clay core. The core is the impervious element, going from the foundations practically until the crest level, and it has slopes 1:1 upstream, and vertical downstream. From the inside to the outside, the dam is built of a clay core, two shoulders built with loams of the area, a transitional draining layer 2 m thick and a 4 m thick protective layer of rockfill -measured horizontally-.

La Pedrera Reservoir Picture

The ground plan length of the dam is 716 m, its height from the foundations is 66.30 m, while on the bed it is 61.30 m. The volume of land with which the dam body was built is 5,547,000 cubic metres. To close the storage area upstream of the dam it was necessary to build three dikes, two of which are on the hills of the right riverbank and the third on the left.

Picture view of the embankment of the main dam and Dike I from the right bank
View of the embankment of the main dam and Dike I from the right bank.

The cross-section of the dam is trapezoidal with slopes of 3.5:1 upstream and 3.0:1 downstream. The dam has it foundations at 45.00 –the bed is 50.00- according to a broken line that goes along the hillside of the natural downstream boundary for the storage area. The height of the crest of the main dam is 110.54 in the area of the abutments and 111.30 at the point half-way between both. It is 9 m wide distributed on a road of 6.0 m with two lanes and two verges measuring 1.50 m each.

Detail of La Pedrera Reservoir

The dam has a complex system of filters and drains built on both shoulders. In order to limit the interstitial pressures during the construction of the dam and when the drawoffs take place, the upstream shoulder was built with four horizontal drains, 1.20 m thick and consisting of two outer layers, 30 cm thick, of filtering material -sand -, and a central one of thicker material -gravels -, 60 cm thick.

On the other hand, when completing the vertical embankment of the clay core, on its downstream face, a vertical chimney drain was made, which goes along practically the whole height of the dam –up to the height of 103.00 - and continues horizontally from the level of the foundations until the end of the shoulder downstream. This chimney drain is made up of two outer layers of filtering material -sand - 1.50 m thick, which protect an inner layer, 4 m thick, consisting of gravels. Four horizontal drains are connected to this chimney drain and consist of a single layer of sand 30 cm thick. Finally, at the foundation level chimney drain is extended by means of a horizontal drain made up of a central layer -2.37 m thick - of rockfill, covered in two layers of filtering material -1.19 m thick – that, in turn, are each covered in a layer of sand – 1.50 m thick-. Outside the shoulder downstream, this filter finishes in a rockfill base that reaches a level of 55.00, on the lower berm of the dam.

La Pedrera Reservoir Picture

The loams that make up the shoulder downstream are covered in a filtering layer -2 m thick measured horizontally- of gravels and a layer of rockfill, also 2 m thick measured horizontally. This shoulder presents two horizontal berms, the lower one located at 55.00 and 5 m wide, while the upper one is located at 88.10 and is 4 m wide.

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